Mix ground hazelnuts, baking powder, and flour together in a large bowl.
In another large bowl, whisk together Nutella and egg. Add flour mixture to the Nutella-egg mixture so that a light and fluffy dough forms.
Using your hands, form the dough into a large ball, wrap in plastic wrap and refrigerate for approx. 60 min.
Pre-heat oven to 180°C/350°F. Form dough into small balls and place on a parchment-lined baking sheet, leaving a 1-cm/0.5-inch. space between each ball. Bake for approx. 10 min. Remove from oven and let cool. Dust with confectioner’s sugar, serve, and enjoy!